Heat exchanger antifoulant

ABSTRACT

Disclosed is a process for reducing the fouling in a heat exchanger in which a hydrocarbon stream is heated or cooled as it passes through the heat exchanger. From 1 to 500 parts per million of an organic hydroxylamine is added to the stream to reduce fouling.

BACKGROUND OF THE INVENTION

The invention relates to heat exchangers, particularly heat exchangersused in the processing of crude oil. More particularly, the inventionrelates to an additive for reducing heat exchanger fouling.

In the processing of petroleum, numerous heat exchangers are utilized toheat or cool process streams. Since refineries typically process verylarge quantities of petroleum ranging from 25,000 to 200,000 or morebarrels per day, the heat exchangers in the refinery represent a verylarge capital investment. After a period of operation, deposits build upon the heat exchanger tubes greatly reducing heat exchanger efficiencyand greatly increasing the energy consumed. Eventually, the heatexchanger must be taken out of operation and the tubes cleaned orreplaced. Increasing heat exchanger efficiency and reducing the amountand rate of fouling can provide tremendous energy savings in refineriesand other facilities that use heat exchangers.

DESCRIPTION OF THE PRIOR ART

Numerous heat exchanger antifoulant additives are well known in the art,for example, U.S. Pat. No. 3,442,791 discloses an antifoulant additivefor petroleum hydrocarbons comprising a disalicylidene propane diamineand an alkylphenol or alkylphenol-formaldehyde condensate. Similarly,U.S. Pat. No. 4,200,518 discloses the use of a polyalkyleneamine as aheat exchanger antifoulant additive.

SUMMARY OF THE INVENTION

A process for reducing heat exchanger fouling in which a liquidhydrocarbon stream is passed through a heat exchanger at a temperaturefrom 0° to 1500° F. wherein from 1 to 500 parts per million of anantifoulant additive is added to said hydrocarbon stream, said additivecomprising an organic hydroxylamine.

DETAILED DESCRIPTION OF THE INVENTION

The heat exchangers utilized in the present invention are of any typewhere deposits accumulate on a heat transfer surface. The most commontype of heat exchanger used is commonly known as a shell and tube heatexchanger.

The hydrocarbon stream passing through the heat exchanger is preferablya crude oil stream. Particularly preferred are petroleum stocks thatcontain reactive hydrocarbons such as olefins, sulfur, and nitrogencompounds. However, any hydrocarbon stream which leads to fouling of theheat exchanger can be utilized in the present invention, particularlyvarious fractions of the crude oil. Generally, the streams passingthrough the heat exchanger will be heated or cooled at temperaturesranging from 0° to 1500° F., preferably 50° to 800° F.

THE ORGANIC HYDROXYLAMINES

Any organic hydroxylamine which prevents fouling can be used in thepresent invention. Preferred are the N,N-dihydrocarbylhydroxylamineswith 1 to 18 carbon atoms in the hydrocarbyl group and more preferably 1to 8 carbon atoms in the hydrocarbyl group. Representative hydrocarbylgroups include alkyl, arylalkyl, alkylaryl, aryl, cycloalkyl, alkylene,and heterocyclic groups. More preferred are theN,N-dialkylhydroxylamines with 1 to 10 and preferably 2 to 6 carbonatoms in each alkyl group. Most preferred is N,N-diethylhydroxylamine.The organic hydroxylamines are generally commercially available or canbe readily synthesized by any skilled chemist. Representativehydroxylamines include: N,N-dimethylhydroxylamine,N,N-diethylhydroxylamine, N,N-dipropylhydroxylamine,N,N-dibutylhydroxylamine, N,N-diamylhydroxylamine,N,N-dihexylhydroxylamine, N,N-dioctylhydroxylamine,N,N-dicyclohexylhydroxylamine, N-hydroxylpiperdine,N-hydroxylmorpholine, N-hydroxyldiethyleneimide sulfide,N,N-diallylhydroxylamine, N,N-dibenzylhydroxylamine, andN,N-di-2-propyn-1-hydroxylamine.

To substantially reduce heat exchanger fouling, an effective amount,generally from 1 to 500 parts per million, preferably 5 to 99 parts permillion, and most preferably 10 to 49 parts per million of theabove-described hydroxylamine is added to the stream passing through theheat exchanger. One surprising feature of the present invention residesin the finding that such small quantities of the above-describedadditive are effective in reducing heat exchanger fouling.

EXAMPLES 1-6 Antifouling Tests

Various compounds, including numerous commercial heat exchangeantifoulants and the organic hydroxylamines of the present inventionwere tested for their antifouling characteristics using a standard ALCORTest Apparatus. This test involves feeding a test stock material at afixed rate and for a fixed period of time and at constant inlettemperature into a tube containing a stainless steel electrically heatedrod while supplying enough heat to the rod to maintain the outlettemperature of the test stock constant. As fouling deposits form on therod, the temperature of the rod must be increased to maintain a constantoutlet temperature of the test stock. The initial rod temperature andfinal rod temperature are measured along with the initial and finalweight of the rod. The increase in rod temperature and the amount ofdeposits on the rod are indicative of the degree and rate of fouling.

Eact test run was for three hours and either no additive was used or 50parts per million of additive was added to the test stock. The inlettemperature of the test stock was maintained at 70° F. and the outlettemperature was maintained at 600° F. for the hydrotreater andhydrofiner feedstocks and at 500° F. for the Eastern Wyoming Crude oilstock. The results are shown below in Table I.

                  TABLE I                                                         ______________________________________                                        Test                               Deposit                                    No.   Test Base Stock and Additive                                                                      ΔT, °F.                                                                   Wt, mg                                     ______________________________________                                              Naphtha Hydrotreater Feedstock                                          1     No Additive          4       15.3                                       2     N,N--Diethylhydroxylamine                                                                         -1       8.5                                        3     Diethylamine         8       11.4                                       4     2,4-Dimethyl-6-tbutyl Phenol                                                                      12       0.2                                              (DuPont Antioxidant No. 30)                                             5     Oronite ORA 502.sup.1                                                                              2       16.0                                       6     Exxon Corexit 214.sup.2                                                                           -2       12.4                                       7     Betz Petromeen AF-111.sup.3                                                                       23       6.8                                        8     Betz Petromeen AF-114.sup.4                                                                       10       10.6                                       9     Nalco 262.sup.5     394      16.9                                             Diesel Hydrofiner Feedstock                                             10    No Additive         43       4.0                                        11    N,N--Diethylhydroxylamine                                                                          5       5.8                                        12    Oronite ORA 502.sup.1                                                                             44       3.5                                              Eastern Wyoming Crude Oil                                               13    No Additive         11       6.0                                        14    N,N--Diethylhydroxylamine                                                                          1       6.8                                        15    Oronite ORA 502.sup.1                                                                             56       2.6                                        16    Exxon Corexit.sup.6 97       2.9                                        ______________________________________                                         .sup.1 A polyisobutylene amine having a molecular weight of approximately     1000 to 2000.                                                                 .sup.2 Believed to be a mixture of polyamine phenolic resin and borated       amide.                                                                        .sup. 3 Believed to be a mixture of phenolic amine polymers, substituted      polymeric amides, and heterocyclic amides in heavy aromatic naphtha.          .sup.4 Believed to be a mixture of substituted polymeric amides in heavy      aromatic naphtha.                                                             .sup.5 Believed to be an ethylenediamine salt of an organic sulfonic acid     .sup.6 Believed to be a mixture of polyamineamides and fatty acid             alkenolsamine esters.                                                    

The above data indicates that the organic hydroxylamines of the presentinvention are generally superior as an antifouling agent compared to theother related compounds and commercial additives tested.

What is claimed is:
 1. A process for reducing heat exchanger fouling inwhich a liquid hydrocarbon stream is passed through a heat exchanger ata temperature from 0° to 1500° F. wherein from 1 to 500 parts permillion of an anti-fouling additive is added to said hydrocarbon stream,said additive consisting essentially of an organic hydroxylamine whereinsaid hydroxylamine is an N,N-dialkylhydroxylamine and wherein saidstream is crude oil or a fraction thereof.
 2. The process of claim 1wherein said N,N-dialkylhydroxylamine has 2 to 6 carbon atoms in thealkyl group.
 3. The process of claim 2 wherein 5 to 99 parts per millionof said additive are added to said stream.
 4. The process of claim 3wherein said hydrocarbon stream is passed through said heat exchanger ata temperature from 50° to 800° F.
 5. The process of claim 2 wherein saidorganic hydroxylamine is N,N-diethylhydroxylamine.
 6. The process ofclaim 5 wherein said heat exchanger is a shell and tube heat exchanger.7. A process for reducing heat exchanger fouling in which a liquidhydrocarbon stream is passed through a heat exchanger at a temperaturefrom 0° to 1500° F. wherein from 1 to 500 parts per million of anantifouling additive is added to said hydrocarbon stream, said additiveconsisting essentially of an organic hydroxylamine wherein saidhydroxylamine is an N,N-dialkylhydroxylamine and wherein said stream iscrude oil and said stream is heated in said heat exchanger.
 8. Theprocess of claim 7 wherein said N,N-dialkylhydroxylamine has 2 to 6carbon atoms in the alkyl group.
 9. The process of claim 8 wherein 5 to99 parts per million of said additive are added to said stream.
 10. Theprocess of claim 9 wherein said hydrocarbon stream is passed throughsaid heat exchanger at a temperature from 50° to 800° F.
 11. The processof claim 10 wherein said organic hydroxylamine isN,N-diethylhydroxylamine.
 12. The process of claim 11 wherein said heatexchanger is a shell and tube heat exchanger.